The function of rabbit lymphoid cells and antibody in immune rejection of Shope Fibroma Virus induced tumors will be studied. The interaction of lymphoid cells in the humoral immune response and the role of lymphoid cells and antibody in tumor immunity have been extensively examined in inbred mice. Studies of other species and different tumors are necessary to determine if the conclusions based on the mouse studies are generally valid. The lymphoid cells which participate in the rabbit humoral immune response will be identified and characterized by techniques similar to those used in studies of the mouse including determination of the functional differences in organ source, identification of cooperative functions in in induction and expression of humoral immunity in vitro and in vivo, and identification of specific surface markers. When rabbit lymphoid cell populations with different immunological functions are identified, the role of these different characterized lymphoid cell populations and humoral antibody in rejection of Shope Fibromas will be determined using 1) in vitro assays for immune effector cells or antibody, 2) the in vitro induction of tumor immunity, and 3) the passive transfer of tumor immunity in vivo. The interaction of antibody and effector cells (blocking antibody, antibody directed cellular cytotoxicity) will be explored. The immune reactivity of normal neonates which are incapable of tumor rejection will be compared to that of normal adults which do mount a successful anti-tumor response. Inbred rabbits will be used for cell transfer experiments and in vitro induction of tumor immunity so that interpretations will not be complicated by allogeneic effects, graft vs. host reactions, or transplantation rejection. The proposed studies should result in a more comprehensive understanding of the mechanisms of tumor immunity.